The utility of spider silk proteins as “super filaments” has led to attempts to produce recombinant spider dragline silks (Prince et al., Biochemistry 34: 10879 –10885, 1995; Fahnestock and Irwin, Appl. Microbiol. Biotechnol. 47: 23 –32, 1997; Fahnestock and Bedzyk, Appl. Microbiol. Biotechnol. 47: 33 –39, 1997). Although successful expression of spider's silk has been demonstrated in E. coli, significant problems remain, such as instability of the sequences used due to recombination and rearrangement in the repetitive areas of the gene, inefficient transcription, translational pausing and premature termination of synthesis resulting in limitations on the length of the silk that can be produced efficiently (less than or equal to 1000 amino acids), low protein yields (4 to 300 mg/liter), and low solubility of the produced fiber.
Production of synthetic spider dragline silk protein in the methylotropic yeast Pichia Pastoris was superior to that of E. coli in that longer proteins of at least 1600 amino acids in length could be produced efficiently with no observed size heterogeneity due to premature termination of synthesis and stability of the repetitive sequences in the genes being expressed. Yields of protein in the Pichia system were 663 mg/liter; however, only 15% of this was in a soluble form in the yeast cell lysate.